Several areas of concentration in this project will contribute to the overall goal of elucidating the regulation of intestinal calcium transport. 1) Investigate the relative roles of cellular and paracellular routes of intestinal calcium transport as modulated by viamin D using transepithelial voltage clamp techniques. 2) Establish the site of action of agents known to influence calcium absorption and secretion (e.g., vitamin D, cyclic nucleotides, hormones, and ATPase inhibitors) with technique indicated above. 3) Define the interaction of the alkaline earth metals (Mg and Sr) with the anamolus calcium secretory mechanism previously identified together with investigations of copper, zinc, and manganese transport using short-circuiting techniques. 4) Continue investigation of calcium influx and efflux mechanisms in isolated microvillus and basolateral membrane vesicles.